Rear extension in Hounslow
Do you need planning permission for a rear extension in Hounslow?
Outside the conservation areas, much of the Victorian and interwar stock keeps permitted development rights for a single-storey rear extension within the limits, or larger via prior approval, to the Residential Extension Guidelines SPD. Inside a conservation area — especially the tightly controlled garden-suburb and park-edge streets — expect a full application. The 2022 small-HMO conversion direction across most of the borough does not itself remove ordinary rear-extension rights.
Chiswick and Isleworth terraces extend under PD outside the conservation areas; Bedford Park and the heritage areas need a full application.
Hounslow is a borough of two halves: heritage-rich Chiswick, Brentford and Isleworth in the east, and more suburban streets toward Heathrow in the west. Conservation areas concentrate in that eastern belt, with householder Article 4 directions in the most sensitive ones. Outside those pockets, rear extensions remain everyday projects on ordinary stock.
What actually applies in Hounslow
Conservation areas in Hounslow
Real · planning.data.gov.ukEvery designated conservation area in Hounslow from the official dataset — inside one, permitted development narrows and design scrutiny rises.
- Bedfont Green
- Bedford Park
- Bedford Park (article 4)
- Chiswick High Road
- Chiswick House
- Cranford Park
- Cranford Village
- Feltham Town Centre
- Glebe Estate
- Grand Union Canal & Boston Manor
- Grand Union Canal and Boston Manor
- Grove Park
- Gunnersbury Park
- Gunnersbury Park (article 4)
- Hanworth Park
- Heston Village
- Hounslow Cavalry Barracks
- Isleworth Riverside
- Kew Bridge
- Old Chiswick
- Osterley Park
- Spring Grove
- St Dunstan's
- St Paul's Brentford
- St Paul's Church
- St Paul's, Brentford
- St Stephen's
- Stamford Brook
- Strand on the Green
- The Butts
- Thorney Hedge
- Turnham Green
- Wellesley Road
- Woodlands Grove
Source: planning.data.gov.uk · Open Government Licence. Boundaries are checked at address level by the area report.
Article 4 directions in Hounslow
Real · planning.data.gov.ukNo householder Article 4 geometry for Hounslow appears in the national planning.data.gov.uk dataset, but the borough operates significant directions: householder Article 4 directions in conservation areas such as Bedford Park and Gunnersbury Park (removing permitted development so even minor external changes need permission), and an HMO Article 4 direction (made 2022) applying across most of the borough. The Residential Extension Guidelines SPD sets householder design expectations. Check the council's Article 4 pages for the position at a specific address.
Source: planning.data.gov.uk · Open Government Licence · 2 directions recorded. Checked at address level by the area report.
Prices: HM Land Registry UK House Price Index, December 2025 · Open Government Licence.
The planning route — PD or permission?
Permitted development (GPDO Class A) covers single-storey rear extensions up to 3m beyond the original rear wall on attached houses and 4m on detached, with a maximum height of 4m. The 'larger home extension' route extends this to 6m/8m through prior approval with neighbour consultation — but that larger route is not available in conservation areas.
In conservation areas, the basic 3m/4m single-storey rear PD allowance usually survives — what conservation-area status removes is side extensions and two-storey rear extensions. An Article 4 direction can remove more, but Camden's directions in Hampstead and Belsize target front-and-side appearance (solar panels, window changes, boundary treatments), not the single-storey rear allowance. Flats have no PD rights at all. Two-storey rear extensions in conservation areas always need full permission.
Practical rule across London: check the address first. If a conservation area or Article 4 direction applies, budget for a full householder application decided on design, neighbour daylight (the 45-degree test) and materials.
Permitted development limits — rear extension
| Single-storey rear depth — attached house | 3m beyond the original rear wall |
| Single-storey rear depth — detached house | 4m beyond the original rear wall |
| Larger extension via prior approval | 6m attached / 8m detached — not in conservation areas |
| Maximum height (single storey) | 4m |
| Two-storey rear in a conservation area | Full planning permission required |
| Flats | No permitted development rights |
Limits summarise the General Permitted Development Order (Schedule 2, Part 1) as it applies in London. In Hounslow, a conservation area, Article 4 direction or listed status changes the route — the panels above show what is designated, and the address check confirms what applies at your property.
How much does a rear extension cost in Hounslow?
| Cost per m² (low — straightforward site) | £3,000 |
| Cost per m² (expected) | £3,800 |
| Cost per m² (high — conservation spec, hard access) | £4,600+ |
| Typical build cost (12–18m² single storey) | £36,000 – £83,000 |
| Professional fees, surveys, party wall (add) | 10–18% of build |
Indicative London ranges calibrated from real project data. Conservation-area specifications (matching stock brick, lime mortar, bespoke glazing) and restricted rear access are the two biggest cost drivers. VAT not included.
Realistic timeline
| Design and drawings | 4–8 weeks |
| Planning decision (full application) | 8–12 weeks (8-week statutory target) |
| Prior approval route, where available | 42 days |
| Party wall agreements | 4–10 weeks (parallel) |
| Build | 3–5 months |
What catches people out in Hounslow
National geometry does not currently hold all of Hounslow's Article 4 directions — confirm conservation-area and HMO positions on the council's pages as well as the free area report. Daylight and party wall issues remain routine hold-ups.
Postcode districts in Hounslow
W4 is Chiswick — Bedford Park (often called the world's first garden suburb, with an Article 4 direction), Chiswick House, Old Chiswick, Turnham Green and Strand on the Green.
W4 — Chiswick & Bedford Park →TW8 is Brentford — the St Paul's Brentford conservation area, the Grand Union Canal and Boston Manor, and Kew Bridge.
TW8 — Brentford →TW7 covers Isleworth — the Isleworth Riverside and Spring Grove conservation areas and Osterley Park's edge.
TW7 — Isleworth →TW3 is central Hounslow — the Cavalry Barracks conservation area and the suburban stock around the town centre.
TW3 — Hounslow →TW13 is Feltham — the Feltham Town Centre and Bedfont Green conservation areas and the western suburbs near Heathrow.
TW13 — Feltham →TW4 is Hounslow West and the Heston fringe — suburban stock away from the Chiswick heritage belt.
TW4 — Hounslow West & Heston fringe →TW5 covers Heston and Cranford in Hounslow — interwar and later suburban housing near the A4 corridor.
TW5 — Heston & Cranford →TW14 covers Feltham and Bedfont in Hounslow (with a Hillingdon edge).
TW14 — Feltham & Bedfont →Rear extension in Hounslow, asked straight
Do I need planning permission for a rear extension in Hounslow?
How much does a rear extension cost in Hounslow?
Does the 2022 small-HMO conversion direction affect rear extensions?
Why is the eastern belt stricter?
Do I need a party wall agreement?
What applies at your address?
Borough-level rules only narrow it down. Enter a Hounslow postcode for the live constraint check — conservation area, Article 4 and sold-price comparables, cited to source.
Need it in writing for one address? A planning permission report for a Hounslow property — from £59, or surveyor-reviewed from £295.
Planning Permission Checker provides planning and cost intelligence for early feasibility only. It is not legal, planning, valuation, architectural, structural, or surveying advice. All estimates are indicative and must be verified by qualified professionals before purchase, design, planning submission, or construction.
Cost estimates are indicative only — not a quotation. Final price depends on survey, specification, structure, access, party wall matters, VAT, professional fees, and contractor availability.
Planning outcomes are not guaranteed. Local planning authorities make final decisions.